where \(\mathbf {\mu }_{0,t}\)  and \(\mathbf {\sigma }_{0,t}\)  are sufficient statistic parameters of the prior. By introducing temporal structure into the prior distribution of the latent variable, the representation power is enhanced. The hidden states are updated with the recurrence equation using gated recurrent unit (GRU) [1]}:
\(\mathbf {h}_t=f_{\theta _{}}\left(\varphi _{\theta _{}}^{\mathbf {z}}(\mathbf {z}_t),\mathbf {h}_{t-1}\right)\) 
